1. Field of the Invention:
The present invention relates to a chloroprene rubber composition. In particular, it relates to a chloroprene rubber composition which is unexpectedly improved in resistance to extraction with an oily matter, cold resistance, heat resistance and other physical and chemical properties.
2. Statement of Prior Arts
Chloroprene rubber compositions have been widely used particularly in the field of automobile rubber components, for example, covering material for various hoses such as fuel hose or brake hose or boots such as synchronous joint boot on dust cover boot. Recently, the circumstances have become severe upon these rubber components owing to the regulation of exhaust gas, the reduction in fuel consumption and the enhancement of engine power, so that a chloroprene rubber composition excellent in heat resistance, non-extractability with oily matter such as oil or grease and cold resistance has been desired.
To satisfy these requirements, improvements which comprise blending rubbers with each other or adding the third component have been examined to exhibit considerable effects. However, each of these improvements has both advantages and disadvantages. No definitive improvement methods have been found as yet.
In the state of arts, a chloroprene rubber having a resistance to oil has been improved in cold resistance by addition of a plasticizer such as di-2-ethylhexyl sebacate (hereinafter referred to as "DOS"), di-2-ethylhexyl adipate (hereinafter referred to as "DOA") or di-2-ethylhexyl azelate (hereinafter referred to as "DOZ"). However, it is well known that any of these plasticizers is extracted with oily matters such as oil or grease in a very short time, thus decreasing the cold resistance remarkably.
Further, it is also known that the cold resistance of chloroprene rubber can be improved by blending a rubber excellent in cold resistance, such as natural rubber (hereinafter referred to as "NR") or polybutadiene rubber (hereinafter referred to as "BR") instead of such a plasticizer. However, this method is disadvantageous in that the blending of a large amount of NR or BR is necessary to improve the cold resistance sufficiently and that the compatibility of rubbers with each other is a source of difficulty.
Furthermore, the addition of polyester plasticizers having a relatively large molecular weight has been examined. Though these polyester plasticizers are not extracted with oily matter such as oil or grease, they cannot give a sufficient cold resistance.
The inventors of the present invention have studied with attention to the fact that a polyalkylene glycol is excellent in cold resistance and have found that an ester derived from a specified glycol component and a specified fatty acid component can form a chloroprene rubber composition excellent in cold resistance when added to chloroprene rubber and that the ester contained in the composition is not extracted with oily matters.